On Thursday, an asteroid the size of a house will be watched carefully by astrophysicists as it hurtles “damn close” to Earth.

The large space rock, named 2012 TC4, was first spotted five years ago by the Pan-STARRS telescope at the Haleakala Observatory, in Hawaii, before disappearing as it orbits the sun. It then reemerged in July on a trajectory well inside our lunar orbit.

Scientists have said the asteroid is on course to pass safely by, just south of Australia, and poses no threat.

However it presents space agencies with a rare opportunity to test the planet’s space defenses and wargame what they would do if a larger, more threatening asteroid was detected heading straight for Earth.

How close will TC4 come to Earth?TC4 is between 50 to 100ft in diameter and traveling through space at roughly 16,000 mph - 4.5 miles a second. It is predicted to start to pass Earth from around 7am GMT on Thursday and will be about 27,000 miles from our atmosphere.

This may sound like a long way away, yet it’s a short distance in planetary terms and around one eighth of the distance between the Earth and the Moon. It is also just above the distance our satellites orbit.

Rolf Densing, who heads the European Space Operations Centre in Darmstadt, Germany said: “It's damn close. The farthest satellites are 36,000 kilometers [22,000 miles] out, so this is indeed a close miss.

“TC4 poses absolutely no threat to the planet, but it does afford a chance to test our asteroid tracking and space defense capabilities”.

Has Earth been struck before?Earth has been struck by asteroids and meteors repeatedly over its 4.5 billion year lifespan, however the chances of a serious incident happening again in our lifetime are remote.

The most famous event was the sixty mile-wide asteroid that struck the coast of Mexico around 65 million years ago and is thought to have lead to the extinction of the dinosaurs. But there have been more recent, less dramatic examples.

Does TC4 pose a threat?Even though TC4’s orbit has been described as ‘damn close’, astrophysicists can now predict asteroids' path to a margin of around 10 miles and are confident TC4 will not come near the Earth’s atmosphere. Even if it were to hit Earth, scientists say it would have an impact similar to that of the Chelyabinsk meteor.

Detlef Koschny, Near-Earth Object segment manager at the ESA, based in the Netherlands, said: “It's [TC4] smaller [than Tunguska], only about 10-20 meters - [we] just got some radar observations [Monday] night. So it's more like Chelyabinsk in 2013. A shock wave possibly shattering windows; possibly a few meteorites falling down.”

Space defensesTC4 does afford space agencies across the globe an opportunity to wargame the planet's space defenses for a scenario where Earth was in the path of a more dangerous asteroid. If an asteroid the size of TC4 or slightly bigger was on course to hit a populated area, agencies such as the ESA and NASA would look to warn people and work with relevant governments to potentially start an evacuation.

However if the agencies detected an object over 130ft approaching they would need to start thinking about deflecting the asteroid from Earth's path.

To do this space agencies would fire a satellite into the asteroid in an attempt to shift its trajectory, in what is known as a "kinetic impactor" method. The asteroid would need to be hit when it was at least two years away to give it time alter its trajectory and clear Earth.

Mr Koschny said: “Yes we have the capability of hitting an asteroid or comet with a satellite. NASA have done that in 2004 with the 'Deep Impact' mission. The difficult thing is the aiming, the Deep Impact target was a comparably large object (a few km). But industry assures us that they could do the same for an object of 100 to 200 meters.”

He added that TC4’s trajectory was only spotted in July due to its relatively small size, but that agencies would more than likely see an asteroid large enough to pose a serious threat to Earth in time to fire a deflector satellite at it. (Source: The Telegraph)